From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ozlabs.org ([203.10.76.45]:61898 "EHLO ozlabs.org") by vger.kernel.org with ESMTP id S265809AbUFSEMJ (ORCPT ); Sat, 19 Jun 2004 00:12:09 -0400 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <16595.48028.925656.212915@cargo.ozlabs.ibm.com> Date: Sat, 19 Jun 2004 14:05:48 +1000 From: Paul Mackerras Subject: Re: Accessing memory remote across the bus in the same way as local memory In-Reply-To: <1087601198.2134.206.camel@mulgrave> References: <1087601198.2134.206.camel@mulgrave> To: James Bottomley Cc: linux-arch@vger.kernel.org List-ID: James Bottomley writes: > The question has come up [in the DMA API issues thread on lkml] of > whether we can access on chip memory areas as though they were normal > memory (i.e. use normal reads and writes to access it). > > The memory regions in question would have to be accessible via MMIO > cycles on the bus and be aligned and sized as multiples of PAGE_SIZE. > > The question is given the constraints, can we pull page table tricks on > every platform to make this bus remote memory look like real memory? Not on iSeries machines (ppc64 machines running OS/400). There we have to do a hypervisor call for every access to PCI memory or I/O space, unfortunately. Fortunately people don't tend to put arbitrary PCI adaptors in iSeries boxes, and they don't run X servers. Linux partitions on iSeries machines are mostly used for things like firewalls and web servers. What did you want to be able to do this for? It probably isn't the end of the world if whatever you want to do with this doesn't work on iSeries. Paul.